1. Field of the Invention
The present invention relates to an apparatus for controlling a moving speed of a magnetic head.
2. Description of the Related Art
Access control for moving a magnetic head of a magnetic disk apparatus to a target track and track following control for positioning the magnetic head in the center of the target track have conventionally been used as positioning control of the magnetic head. The access control is also called speed control since a moving speed of the magnetic head is controlled.
In the speed control, a target speed corresponding to a distance by which the magnetic head moves to the target track, is preset to make the actual moving speed of the magnetic head coincident with the preset target speed. More specifically, an actual moving speed value is obtained by sequentially detecting and computing the current positions of the magnetic head during the movement of the magnetic head, and a value obtained by subtracting the target speed value from the moving speed value, i.e., a differential speed value representing a difference between the moving speed value and target speed value is fed back to a speed control output. Closed-loop control is thus performed.
In the closed-loop control, the moving time of the magnetic head when the differential speed value is positive differs from that of the magnetic head when it is negative. When the differential speed value is positive, a period of time until the magnetic head reaches the target track after the magnetic head starts to move, i.e., the moving time is shorter than the target moving time. When the differential speed value is negative, the moving time is longer than the target moving time. Even though the precision of the speed control, that is, the absolute value of the differential speed value is the same, the moving time changes in accordance with the polarity of the differential speed value, and shortening and stabilization of the moving speed of the magnetic head according to the original object cannot be accomplished.
It is therefore desirable to provide an apparatus for controlling a moving speed of a magnetic head which is capable of stably moving the magnetic head and shortening the moving time thereof.